What is public key cryptography?

Public key cryptography (PKC), also known as asymmetric cryptography, is a mechanism that uses both public and private keys, as opposed to symmetric cryptography which uses a single key. The use of key pairs gives PKC unique capabilities and features to address inherent challenges in other cryptographic techniques. This form of cryptography has become an important principle in modern computer security and a key component of the growing cryptocurrency ecosystem.

How Public Key Cryptography Works

In the PKC system, the sender uses the public key to encrypt information, while the receiver uses the private key to decrypt information. Since the two keys are completely different, the public key can be shared safely without worrying about compromising the security of the private key. Each asymmetric key pair is unique, so it ensures that information encrypted with the public key can only be read by the person holding the corresponding private key.

And, because the key pairs generated by asymmetric encryption algorithms are mathematically related, their key lengths are much longer than those used in symmetric cryptography. They are usually 1024 or 2048 bits long, so it is extremely difficult to use a public key to calculate the corresponding private key. Today, the most common asymmetric encryption algorithm is called RSA. In the RSA scheme, the key is generated by multiplying two numbers (usually two large prime numbers) to get a public modulus. The modulus will generate two keys, a public key that can be shared, and a private key that needs to be kept secret. The RSA algorithm was first proposed in 1977 by Rivest, Shamir, and Adleman (hence RSA), and it is still an important part of public key cryptography systems.

Using PKC as an encryption tool

Public key cryptography solves a long-standing problem in symmetric algorithms, namely the communication problem between encryption keys and decryption keys. Sending a symmetric key over an insecure connection risks exposing it to a third party, who can then read any information encrypted with the shared key. While cryptographic techniques exist to address this problem, such as the Diffie-Hellman key exchange protocol, these keys are still vulnerable. In public key cryptography, this problem does not exist at all, and the key used for encryption can be shared over any network connection. Thus, asymmetric algorithms offer a higher level of protection than symmetric algorithms.

Use cases in digital signatures

Another application of asymmetric cryptography is to use digital signatures to authenticate data. Essentially, a digital signature is a hash created using the data in a message. Once the message is sent, the recipient can verify the signature using the sender's public key to verify the origin of the message and ensure that the message has not been tampered with. In some cases, digital signatures and encryption are used together because the hash itself may also be encrypted. However, it is important to note that not all digital signature schemes use encryption.

limitation

Indeed, PKC can be used to improve computer security and verify the integrity of information, but it also has certain limitations. Because encryption and decryption involve complex mathematical operations, asymmetric algorithms can also be slow when processing large amounts of data. And this type of cryptography also relies heavily on the assumption that private keys are kept confidential. If a private key is accidentally shared or made public, the security of information encrypted with its corresponding public key will be compromised. Sometimes a user's private key can also be accidentally lost, in which case the user will lose access to the encrypted data.

Applications of Public Key Cryptography

This type of cryptography is used by many modern computer systems to provide security for sensitive information. For example, public key cryptography can be used to encrypt emails to ensure the confidentiality of their contents. The Secure Sockets Layer (SSL) protocol, which allows websites to connect securely, also uses asymmetric cryptography. PKC systems are also being explored for secure electronic voting environments (such electronic voting environments would allow voters to participate in elections on their home computers).

The characteristics of PKC also stand out in blockchain and cryptocurrency technology. When a new cryptocurrency wallet is created, a pair of keys (public and private) are generated. Public addresses are generated using the public key and can be safely shared with others. On the other hand, the private key is used to create digital signatures and verify transactions, so it must be kept secret. Once the transaction is verified by the authentication hash in the digital signature, it can be added to the blockchain ledger. This digital signature system ensures that only the user who has the corresponding private key of the cryptocurrency wallet can access the funds from the wallet. But it is worth noting that the asymmetric cryptography used in cryptocurrency applications is different from that used for computer security purposes. For example, Bitcoin and Ethereum use the Elliptic Curve Digital Signature Algorithm (ECDSA) to verify transactions.

From computer security to verifying cryptocurrency transactions, public key cryptography plays a key role in securing modern digital systems. By using pairs of public and private keys, asymmetric cryptography algorithms address the security issues inherent in symmetric cryptography. PKC has been used for many years and is constantly being developed in emerging fields, especially blockchain and cryptocurrency.